A study of the prostate, androgens and sexual activity of male rats

Abstract

Background: The prostate is a sexual gland that produces important substances for the potency of sperm to fertilize eggs within the female reproductive tract, and is under complex endocrine control. Taking advantage of the peculiar behavioral pattern of copulating male rats, we developed experimental paradigms to determine the influence of sexual behavior on the level of serum testosterone, prostate androgen receptors, and mRNA for androgen receptors in male rats displaying up to four consecutive ejaculations.

Methods: The effect of four consecutive ejaculations was investigated by determining levels of (i) testosterone in serum by solid phase RIA, (ii) androgen receptors at the ventral prostate with Western Blots, and (iii) androgen receptors-mRNA with RT-PCR. Data were analyzed with a one-way ANOVA followed by a post hoc application of Dunnett's test if required.

Results: The constant execution of sexual behavior did not produce any change in the weight of the ventral prostate. Serum testosterone increased after the second ejaculation, and remained elevated even after four ejaculations. The androgen receptor at the ventral prostate was higher after the first to third ejaculations, but returned suddenly to baseline levels after the fourth ejaculation. The level of mRNA increased after the first ejaculation, continued to increase after the second, and reached the highest peak after the third ejaculation; however, it returned suddenly to baseline levels after the fourth ejaculation.

Conclusion: Four consecutive ejaculations by sexually experienced male rats had important effects on the physiological responses of the ventral prostate. Fast responses were induced as a result of sexual behavior that involved an increase and decrease in androgen receptors after one and four ejaculations, respectively. However, a progressive response was observed in the elevation of mRNA for androgen receptors, which also showed a fast decrease after four ejaculations. All of these changes with the prostate gland occurred in the presence of a sustained elevation of testosterone in the serum that started after two ejaculations. A consideration of these fast-induced changes suggests that the nerve supply plays a key role in prostate physiology during the sexual behavior of male rats.

Figure 1

The hit rate parameter. The quantification of sexual behavior in male rats includes the recording of several parameters. Two of the most important are the frequency of mounts (FM) and frequency of intromissions (FI). The computation of FI/(FM+FI) results in a value representing the hit rate, which reflects the potency of males with respect to the execution of sexual behavior. Figure shows this parameter as measured for experimental males, and indicates that the execution of sexual behavior was stable across consecutive ejaculations and in the range acceptable for sexually experienced males.

Figure 2

Weight of the ventral prostate in sexually active male rats. The graph shows that the weight of the ventral prostate was not affected by consecutive ejaculations, indicating that sexual experience and constant copulation did not impact its size.

Figure 3

Testosterone in serum after consecutive ejaculations. The graph shows the basal level of testosterone in sexually experienced male rats before entering a sexual test (white bar). No effect was observed in this level after one ejaculation. However, the level increased to the highest value after the second and subsequent ejaculations. ** = p < 0.01.

Figure 4

Androgen receptors at the ventral prostate. The execution of consecutive ejaculations had a strong impact on the level of androgen receptors at the ventral prostate. The graph shows that the protein for androgen receptors was detected in males that were not copulating (white bar). However, the concentration increased to its highest value after ejaculations one to three, and then returned to baseline levels after four ejaculations. Western blots at the top show bands for β-actin (β-Ac) and the androgen receptor (AR); mw = molecular weight; 1–4 = number of ejaculations. ** = p < 0.01.

Figure 5

mRNA for androgen receptors at the ventral prostate. The level of mRNA for androgen receptors at the ventral prostate was modulated by copulation. The graph shows that mRNA was detected in males before sexual behavior (white bar). The level of mRNA increased constantly during the first three ejaculations, reaching the highest value after the third ejaculation. However, the concentration returned to baseline levels after four ejaculations. RT-PCR gels at the top show bands of mRNA for β-actin (β-Ac mRNA) and the androgen receptor (mRNA AR); bp = base pair; 1–4 = number of ejaculations. * = p < 0.05; ** = p < 0.01.